This invention relates to television receiver arrangements of a kind suitable for use in a television transmission system of a character in which coded data pulses representing alpha-numeric text or other message information are transmitted in a video signal in at least one television line in field-blanking intervals where no picture signals representing normal picture information are present, said television receiver arrangement including data selection and acquisition means for extracting selectively coded data pulses from a received video signal, a data store for storing the extracted coded data pulses, decoding means for producing from the stored coded data pulses a video signal which can be used to cause the display on a television screen of the particular message information represented by the stored coded data pulses, and oscillator means for producing locally generated synchronising signals within the television receiver arrangement itself, which locally generated synchronising signals can be used for the television display.
The television receiver arrangement may include suitable television display means, or it may be adapted to feed the video signal into a separate television receiver.
A television transmission system of the character referred to above is described in United Kingdom patent specification No. 1,370,535.
A television receiver arrangement of the above kind is known from Mullard Technical Information Article 34, dated September, 1976.
The use of oscillator means within a television receiver arrangement of the above kind to produce locally generated synchronising signals is also known from German Offenlegungshrift No. 26 51 635 in which the locally generated synchronising signals are produced for the television display of stored data in the absence of television synchronisation normally received (e.g. from a broadcast video signal containing synchronizing signals which can be separated out). The stored data which is for display may have been received either from a television video signal, or from a normal telephone transmission line. The television receiver arrangement described in this German Offenlegungsschrift is also organised such that it blocks the operation of a television synchronising separation stage and instead produces locally generated synchronising signals when a received television signal falls below a predetermined threshold level.